Bimar DEU322 Notice D'instructions page 47

(by means of shut off valves) in a part of the system remote
from the leak. Oxygen free nitrogen (ofn) shall then be
purged through the system both before and during the
brazing process.
Removal and evavuation. When breaking into the refrigerant
circuit to make repairs or for any other purpose conventional
procedures shall be used. However, it is important that best
practice is followed since flammability is a consideration. The
following procedure shall be adhered to:
Remove refrigerant;
Purge the circuit with inert gas;
Evacuate;
Purge again with inert gas;
Open the circuit by cutting or brazing.
The refrigerant charge shall be recovered into the correct recovery
cylinders.
The system shall be flushed with OFN to render the unit safe.
This process may need to be repeated several times. Compressed
air or oxygen shall not be used for this task.
Flushing shall be achieved by breaking the vacuum in the system
with ofn and continuing to fill until the working pressure is
achieved, then venting to atmosphere, and finally pulling down
to a vacuum. This process shall be repeated until no refrigerant is
within the system. When the final OFN charge is used, the
system shall be vented down to atmospheric pressure to enable
work to take place. This operation is absolutely vital if brazing
operations on the pipe-work are to take place. Ensure that the
outlet for the vacuum pump is not close to any ignition sources
and there is ventilation available.